Neurocrine Biosciences Shares New Long-Term Data for VYKAT XR in Prader-Willi Syndrome at ENDO 2026

Neurocrine Biosciences has announced new late-breaking data from the Phase 3 development program of VYKAT XR (diazoxide choline) extended-release tablets at ENDO 2026. The latest findings show that individuals with Prader-Willi syndrome (PWS) who restarted treatment after a temporary withdrawal period experienced lasting improvements in hyperphagia and other behavioral symptoms associated with the condition.

The results add to the growing body of evidence supporting the long-term effectiveness of VYKAT XR in patients aged four years and older living with PWS.

According to Sanjay Keswani, Chief Medical Officer at Neurocrine Biosciences, the new data further strengthen confidence in VYKAT XR as a long-term treatment option for hyperphagia, one of the most challenging symptoms faced by people with Prader-Willi syndrome.

Understanding the Phase 3 Development Program

The VYKAT XR clinical development program was conducted in several stages over multiple years.

The program included a randomized, double-blind placebo-controlled study known as C601, followed by an open-label extension study called C602. After that, participants entered a 16-week randomized withdrawal phase before continuing into the long-term open-label extension study known as C614.

Researchers used this approach to better understand both the immediate and long-term effects of treatment.

Study C614 Evaluated Long-Term Treatment Outcomes

The latest data come from Study C614, which enrolled 77 participants with a mean age of 15.3 years. More than half of the participants were female.

The study focused on two important questions. First, researchers wanted to know whether patients who had been switched to placebo during the withdrawal phase could regain treatment benefits after restarting VYKAT XR. Second, they wanted to determine whether patients who remained on continuous treatment could maintain improvements over time.

Researchers evaluated hyperphagia using the Hyperphagia Questionnaire for Clinical Trials (HQ-CT) and assessed behavioral symptoms through the Prader-Willi Syndrome Profile (PWSP). Body mass index (BMI) and long-term safety were also monitored throughout the study.

Patients Regained Benefits After Restarting Treatment

The results showed that participants who restarted VYKAT XR after receiving placebo during the withdrawal period experienced noticeable improvements in hyperphagia.

By Week 13 after resuming treatment, patients demonstrated meaningful reductions in HQ-CT scores. These improvements continued through Week 26 and remained evident after two years of treatment.

The findings suggest that patients who temporarily lost treatment benefits during withdrawal were able to recover those benefits after restarting therapy.

Continuous Treatment Helped Maintain Improvements

Patients who remained on VYKAT XR throughout the study also continued to benefit from treatment.

Although the improvements were smaller compared with those restarting therapy, reductions in hyperphagia remained stable through Week 26 and continued over the two-year follow-up period.

These findings highlight the value of uninterrupted treatment for maintaining long-term symptom control in individuals with PWS.

Behavioral Symptoms Also Improved Over Time

Beyond hyperphagia, researchers observed improvements across all six behavioral domains measured by the PWSP questionnaire among patients who restarted treatment.

Behavioral challenges are a major part of life with Prader-Willi syndrome and often affect both patients and caregivers. The observed improvements suggest that VYKAT XR may provide broader benefits beyond controlling hunger-related symptoms.

Researchers also reported that body mass index remained relatively stable during long-term treatment.

Additional ENDO 2026 Data Compared VYKAT XR With Real-World Outcomes

Researchers also presented data comparing patients treated with VYKAT XR to participants from the PATH for PWS Natural History Study, a large real-world database that tracks disease progression in people with Prader-Willi syndrome.

Sustained Hyperphagia Improvements Over Three Years

The analysis compared 125 VYKAT XR-treated patients with 229 participants from the PATH study.

Results showed that patients receiving VYKAT XR experienced significantly greater improvements in hyperphagia than those in the natural history cohort. The treatment advantage remained consistent across all evaluated time points, including Year 1, Year 2, and Year 3.

Researchers reported highly significant statistical results throughout the three-year analysis period.

Long-Term Behavioral Benefits Observed

A separate analysis evaluated behavioral outcomes in 105 VYKAT XR-treated participants and 182 individuals from the PATH study.

Across all six behavioral domains, VYKAT XR demonstrated significantly better outcomes than the natural history group over three years.

The largest improvements were observed in anxiety, rigidity and irritability, compulsive behaviors, aggressive behaviors, disordered thinking, and depression.

The findings suggest that long-term treatment may help address several important behavioral challenges associated with Prader-Willi syndrome.

About Prader-Willi Syndrome

Prader-Willi syndrome is a rare genetic neurodevelopmental disorder caused by abnormalities involving chromosome 15.

One of the most defining features of the condition is hyperphagia, a persistent and overwhelming feeling of hunger that is difficult to control. Individuals with PWS often experience constant food-related thoughts, intense food-seeking behaviors, and an inability to feel full after eating.

These symptoms can create serious health risks, including obesity, diabetes, cardiovascular disease, choking incidents, and other life-threatening complications.

The Prader-Willi Syndrome Association USA estimates that the condition affects approximately one in every 15,000 live births.

VYKAT XR Approved for Hyperphagia in PWS

VYKAT XR received approval from the U.S. Food and Drug Administration in March 2025 and is commercially available in the United States.

The treatment is indicated for hyperphagia in adults and children aged four years and older with Prader-Willi syndrome.

The medication is contraindicated in patients with known hypersensitivity to diazoxide, thiazides, or any component of the product.

Safety Profile Remains Consistent

The long-term study found that VYKAT XR continued to demonstrate a consistent safety profile.

The most commonly reported adverse reactions include hypertrichosis, edema, hyperglycemia, and rash.

Healthcare providers are advised to monitor blood glucose levels before and during treatment because hyperglycemia, including diabetic ketoacidosis, has been reported in some patients.

Patients should also be monitored for signs of fluid retention and edema, particularly those with underlying cardiac conditions.

Neurocrine Biosciences Continues Focus on Rare and Neurological Disorders

Neurocrine Biosciences is a biopharmaceutical company focused on developing therapies for neurological, psychiatric, endocrine, and immunological disorders.

Its portfolio includes approved treatments for tardive dyskinesia, Huntington’s disease-related chorea, congenital adrenal hyperplasia, hyperphagia associated with Prader-Willi syndrome, endometriosis, and uterine fibroids. The company also maintains a broad pipeline of investigational therapies across multiple therapeutic areas.

The latest VYKAT XR data presented at ENDO 2026 further expand the evidence supporting long-term treatment benefits for individuals living with Prader-Willi syndrome and the challenges associated with chronic hyperphagia.